A friend has a Samsung tv that is 75" 4k JU7100 4k UHD. It has dark area that run across the screen horizontally, about 8 inches, then a brighter area about 8 inches, then again a lighter area. It continues on down the screen. I went to the tv support area and screen test. All the internal pictures showed the same thing. So I dont think it is caused by an external source.
I just chatted with samsung and their next step is a service call. It no longer has warranty. Does anyone know what would cause this? It like rows of backlights are not working.
The attached pic is correct side up on my computer. Not sure why its upside down. Turned it upside down on my computer and uploaded. But still shows upside down here.

I seem to recall, and I may be wrong, that the JU series were an edge array vs the JS series that were the full array backlight. While LED failure is more common than people like to admit, given that you have a Samsung it is more than likely to be a board failure. Samsung uses cheap components on their boards, and they do a poor job of soldering them on. If it proves to be a board, you should be up and running again for 3 or 4 hundred bucks.

Looks like bad LED's to me. Could also be a bad diffuser. I had a 70" Sony that had that issue but in the center top to bottom. I removed the panel, The LED's were OK but you could tell there was a defect in the diffuser. Went to the dump(parts went to eBay). BTW, you should always run the backlights as low as you can stand. I repair a fair amount of LED issues(all brands) and find when powered on, the backlight is set to max.

Turns out he got the extended warranty from Best Buy. Not sure when they will be out to look at it. But if they can't fix it, he will be getting a new one. He paid $3,500. So we will see if he can apply that to another tv. They have nice sony 75" 4k, or the 65" OLED LG. Not sure how long those OLEDs will last though.
I have two sony LCD's, both with excellent picture. A 2007, and a 2009 both never been serviced. Much more natural color than this samsung.

Personally, I would get the OLED. They are not perfect, but the image quality is breathtaking. The Sony TV's are actually made by Samsung, and after selling their lousy products for several years, I hate Samsung with a burning passion.